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Specific Process Knowledge/Thin film deposition/Deposition of Silicon Oxide/Deposition of Silicon Oxide using LPCVD TEOS: Difference between revisions

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TEOS is is Tetra-Ethyl-Ortho-Silicate, sometimes also referred to as Tetra-Ethoxy-Silane, and it has the chemical formula Si(C<sub>2</sub>H<sub>5</sub>O)<sub>4</sub>. It is a liquid that is stored in a bubbler. When a deposition is started, the bubbler is heated to 75 C, and TEOS is then vaporized and introduced into the furnace.  
TEOS is is Tetra-Ethyl-Ortho-Silicate, sometimes also referred to as Tetra-Ethoxy-Silane, and it has the chemical formula Si(C<sub>2</sub>H<sub>5</sub>O)<sub>4</sub>. It is a liquid that is stored in a bubbler. When a deposition is started, the bubbler is heated to 75 C, and TEOS is then vaporized and introduced into the furnace.  


In the furnace, TEOS is thermally decomposed on the sample surface, so that a layer of silicon oxide (SiO<sub>2</sub>) is deposited on the wafer surface:
In the furnace, TEOS is thermally decomposed on the sample surface, so that a layer of silicon dioxide (SiO<sub>2</sub>) is deposited on the wafer surface:


Si(C<sub>2</sub>H<sub>5</sub>O)<sub>4</sub> ''(l)'' → SiO<sub>2</sub> ''(s)'' + 4 CH<sub>2</sub>H<sub>4</sub> ''(g)'' + 2 H<sub>2</sub>O ''(g)''
Si(C<sub>2</sub>H<sub>5</sub>O)<sub>4</sub> ''(l)'' → SiO<sub>2</sub> ''(s)'' + 4 CH<sub>2</sub>H<sub>4</sub> ''(g)'' + 2 H<sub>2</sub>O ''(g)''
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Carbon can be incorporated in the film, but this can be reduced by an annealing.
Carbon can be incorporated in the film, but this can be reduced by an annealing.


The difference between TEOS and silane (used for deposition of silicon nitrid) is essentially that in TEOS the silicon atom is already oxidized. Therefore the conversion of TEOS to silicon dioxide is a rearrangement rather than an oxidation. As can be seen from figure 1 what is basically required to deposit silicon dioxide is a removal of two oxygen atoms for that a relative high temperature of 725 <sup>o</sup>C.     
The difference between TEOS and silane gas (used for deposition of silicon nitride) is essentially that in TEOS the silicon atom is already oxidized. Therefore the conversion of TEOS to silicon dioxide is a rearrangement rather than an oxidation. As can be seen from figure 1 what is basically required to deposit silicon dioxide is a removal of two oxygen atoms, and that to happen a relative high temperature of 725 <sup>o</sup>C is needed.     


There one standard process for deposition on the LPCVD TEOS furnace called TEOS. Anyway there are two standby recipe, which used for load and unload the wafers : one called "Standby" for standard process and other one called "Stb-slw" which is for unloading thicker oxides. And on this recipe the furnace will be opened significantly slower than normal standby recipe. Thick TEOS layers have a tendency to form cracks when they are moved to fast out from the furnace.
TEOS has a very high surface mobility enabling it to fill holes that has a large aspect ratio and leaving the surface quite smooth see figure 2, hence it also covers corners and side walls very well.


TEOS can be used as an alternative to thermally grown or PECVD oxide, it has a dielectric constant of 3.56 (For thermal oxide it is 3.46). Furthermore TEOS has a very high surface mobility enabling it to fill holes that has a large aspect ratio and leaving the surface quite smooth see figure 2, hence it also covers corners and side walls very well.
There one standard process for deposition on the LPCVD TEOS oxide on the furnace, and this recipe is called "TEOS". On the furnace there are also two standby recipes, which are used for wafer loading and unloading. One standby recipe is called "STANDBY". The other standby recipe is called "STB-SLOW", and this is being used, if a thicker TEOS oxide layer (> 1 µm), because the furnace then has to open slowed to avoid stress and this cracks in the deposited film..
 
TEOS can be used as an alternative to thermally grown or PECVD oxide, but this is not at option at DTU Nanolab at the moment.


==Process parameters for the two standard deposition recipes on the TEOS furnace:==
==Process parameters for the two standard deposition recipes on the TEOS furnace:==
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